EP3553923A1

EP3553923A1 - Brushless motor and electrically powered tool

Info

Publication number: EP3553923A1
Application number: EP17878979.8A
Authority: EP
Inventors: Kota Kitamura; Hidenori Shimizu; Koichi Hashimoto; Atsushi Takeyama; Tsuyoshi Yamane
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2016-12-07
Filing date: 2017-09-07
Publication date: 2019-10-16
Anticipated expiration: 2037-09-07
Also published as: JP2018098819A; EP3553923A4; EP3553923B1; JP6827198B2; WO2018105186A1

Abstract

A stator core (31) includes an annular yoke part (32) and a plurality of teeth parts (33) projecting from an inner circumferential surface of the yoke part (32). An insulator (41) covers the yoke part (32) and the teeth part (33) for insulation from a coil part. A rotor (7) is located inward of the stator core (31) across a predetermined interval from an end of the teeth part (33). A protective member (20) is located between the yoke part (32) and the rotor (7) and houses the rotor (7). An end of the teeth part (33) and the protective member (20) form a closed space that houses the rotor (7).

Description

The present disclosure relates to a brushless motor of an inner rotor type.
Japanese Unexamined Patent Application Publication No. 2016-86579 discloses a brushless motor of an inner rotor type used as a driving source for an electric power tool such as a drill driver and an impact driver. The brushless motor disclosed in Japanese Unexamined Patent Application Publication No. 2016-86579 is comprised of a stator core, an insulator, a coil, a rotor, a shaft, and a fan, and the stator core is fixed to the motor housing or the tool main body.
In a brushless motor of an inner rotor type, the rotor is rotatably provided radially inward of the stator core and at a predetermined interval (air gap) from the stator core. The fan has the role of cooling the coil by being rotated in tandem with the shaft to induce a flux of air.
According to the brushless motor disclosed in Japanese Unexamined Patent Application Publication No. 2016-86579 , the fan also sends air to the air gap between the rotor and the stator core so that the dust may be collected on the rotor or the stator core. It should particularly be noted that, if metallic powder is sent along with air, the motor property may be deteriorated as the metallic powder is adsorbed to the magnet on the rotor side.
The disclosure addresses the above-described issue, and a general purpose thereof is to provide a structure capable of preventing foreign materials from entering the air gap between the rotor and the stator core without inhibiting the performance of cooling the coil.
A brushless motor according to an embodiment of the present disclosure includes: a stator core including an annular yoke part and a plurality of teeth parts projecting from an inner circumferential surface of the yoke part; an insulator that covers the yoke part and the teeth part; a coil wound around the insulator that covers the teeth part; a rotor located inward of the stator core at a predetermined interval from an end of the teeth part; and a protective member located between the yoke part and the rotor and housing the rotor.
Another embodiment of the present disclosure relates to an electric power tool including, in a housing, a fan, a brushless motor, and a driving block that includes a power transmission unit for transmitting a rotational force of the brushless motor to a front-end tool. The brushless motor includes: a stator core including an annular yoke part and a plurality of teeth parts projecting from an inner circumferential surface of the yoke part; an insulator that covers the yoke part and the teeth part; a coil wound around the insulator that covers the teeth part; a rotor located inward of the stator core at a predetermined interval from an end of the teeth part; and a protective member located between the yoke part and the rotor and housing the rotor.

Fig. 1 is an overview of an electric power tool according to an embodiment;
Fig. 2 is a perspective view showing an axial cross section of the motor;
Fig. 3 shows an exemplary structure of the protective member;
Fig. 4 shows a cross section of the motor perpendicular to the axis; and
Fig. 5 shows a variation of the protective member.

Fig. 1 is a schematic view of a part of an electric power tool according to an embodiment of the disclosure. The electric power tool 1 includes, in a housing 2, a fan 3 located toward the rear end, a motor 4 located in front of the fan 3, a circuit board 5 located in front of the motor 4, and a driving block 8 located in front of the circuit board 5. The driving block 8 includes an output shaft 9. A chuck mechanism 10 is coupled to the output shaft 9 so that a front-end tool such as a drill and a driver is attachable. The driving block 8 includes a power transmission unit that transmits the rotational force of the motor 4 to the front-end tool. The grip of the housing 2 is provided with a user operation switch 11 manipulated by the operator. When the operator pulls the user operation switch 11, the motor 4 is rotated, and the output shaft 9 of the driving block 8 drives the front-end tool.
The motor 4 is a brushless motor of an inner rotor type and includes a stator 6 fixed to the housing 2, a rotor 7 including a plurality of permanent magnets, and a shaft 12. The shaft 12 is attached to the rotor 7 and is rotatably supported by bearings 13a, 13b fixed directly or indirectly to the housing 2.
The stator 6 is comprised of a stator core and an insulator that covers the stator core. A coil is wound around the insulator that covers the teeth part of the stator core to form a coil part 14 for magnetizing the teeth part. The rotor 7 is located inward of the stator core at a predetermined interval (air gap) from the end of the teeth part.
The circuit board 5 carries a switching element such as a field effect transistor (FET) and an insulated gate bipolar transistor (IGBT) to build an inverter circuit and supplies a driving current to the coil part 14 of the stator 6. The circuit board 5 includes an opening for guiding the shaft 12, and the gap between the opening and the shaft 12 forms a flow passage for the cooling air.
The driving block 8 includes a substantially hollow cylindrical gear case, and the gear case is fixed to a support member provided in the housing 2 as a projection (not shown). A power transmission unit that transmits the rotational force of the motor 4 to the front-end tool attached to the chuck mechanism 10 is provided in the gear case. The power transmission unit may include a planetary gear deceleration mechanism in mesh with a pinion gear fitted to the shaft 12.
A plurality of air inlet ports 15 are formed in the housing 2 to the side of or in front of the driving block 8. For example, the air inlet port 15 may be a rectangular slit. A plurality of air outlet ports 16 are formed toward the back end of the housing 2.
The fan 3 is coupled to the shaft 12 behind the motor 4 and is rotated in tandem with the shaft 12. When the operator pulls the user operation switch 11, the shaft 12 is rotated and the fan 3 is rotated accordingly. The arrow A denotes the flow of air taken into the housing 2 from the air inlet port 15 as the fan 3 is rotated. The air flowing in from the air inlet ports 15, cools the side of the driving block 8 and the circuit board 5, passes through the gap between the opening at the center of the circuit board 5 and shaft 12, cools the coil part 14 of the stator 6, and is discharged outside from the air outlet ports 16. The air inlet ports 15 may be formed in the neighborhood of the circuit board 5 to increase the efficiency of cooling the circuit board 5. The air flowing in from the air inlet port 15 may pass through a flow passage other than the gap between the opening at the center of the circuit board 5 and the shaft 12 to cool the coil part 14.
The motor 4 according to the embodiment includes a protective member 20 that houses the rotor 7 and is located between the yoke part of the stator 6 and the rotor 7. The fan 3 is located outward of the protective member 20, and the protective member 20 forms a cylindrical closed space that houses the rotor 7 without being interposed between the end face of the teeth part of the stator 6 and the rotor 7. The protective member 20 restricts the inflow of air to the air gap between the rotor 7 and the end of the teeth part and prevents foreign materials from entering the space, by enclosing the rotor 7 in the cylindrical closed space. The term "closed space" shall mean a substantially closed space. A hole for dissipating heat may be formed in a part. In essence, the cylindrical closed space formed by the protective member 20 may be configured to house the rotor 7 and to substantially restrict the inflow of air to prevent foreign materials from entering inside.
The protective member 20 forms the cylindrical closed space radially inward of the coil part 14 provided in the teeth part. This causes the coil part 14 to be located outward of the protective member 20 so that the cooling by the air flow is not impeded.
Fig. 2 is a perspective view showing an axial cross section of the motor 4 according to the embodiment. The motor 4 includes the stator 6, the rotor 7, and the shaft 12. For ease of view, illustration of the coil part 14 is omitted.
The stator 6 is comprised of a stator core 31 and an insulator 41 that insulates the stator core 31 from the coil part 14 electrically. The stator core 31 includes an annular yoke part 32 and a plurality of teeth parts 33 that projects radially inward from the inner circumferential surface of the yoke part 32. The insulator 41 includes a yoke insulation part 42 that insulates the yoke part 32 from the coil part 14 and a teeth insulation part 43 that insulates the teeth part 33 from the coil part 14.
The insulator 41 is comprised of two insulator parts 41a, 41b set in the stator core 31 from above and below. Referring to Fig. 2, the insulator parts 41a, 41b are set in the stator core 31 at a distance from each other. Alternatively, the insulator parts 41a, 41b may be set such that they are in contact with each other. Even if the insulator parts 41a, 41b are spaced apart so that a part of the stator core 31 is exposed, the yoke insulation part 42 is located radially inward of the yoke part 32, and the coil is tightly wound around the teeth insulation part 43 projecting away from the teeth part 33 in the circumferential direction. Therefore, insulation between the coil part 14 and the stator core 31 is not impaired.
The rotor 7 is a member rotated around the central axis of the yoke part 32 and is located radially inward of the stator core 31 at a predetermined interval from the end of the teeth part 33. The rotor 7 includes a columnar rotor core 18 and a plurality of permanent magnets 19 located in the rotor core 18. The shaft 12 is fixed to the rotor core 18 and is rotated in tandem with the rotor 7.
The protective member 20 according to the embodiment is comprised of the first protective member 20a and the second protective member 20b. The first protective member 20a and the second protective member 20b house the rotor 7 in the cylindrical closed space by sandwiching the rotor 7 from above and below and being latched to each other.
Fig. 3 shows an exemplary structure of the first protective member 20a and the second protective member 20b. In Fig. 3, illustration of the rotor 7 and the coil part 14 is omitted. The innermost circumference of the stator 6 is comprised of the end of the teeth part 33 and the end of the teeth insulation part 43. As illustrated, the end of the teeth insulation part 43 includes a rising part 44 that rises in the axial direction to prevent the coil from being unwound. The first protective member 20a and the second protective member 20b are configured to have a shape fitted to the rising part 44 of the teeth insulation part 43.
The first protective member 20a includes a lid part 51 having a substantially cylindrical outer circumference and a plurality of wall parts 50 extending from the outer circumference of the lid part 51 in the axial direction. The lid part 51 forms the end face of the cylindrical closed space that houses the rotor 7. A shaft guide hole 52 in which the shaft 12 is inserted is formed in the lid part 51. The wall parts 50 are stuck between the teeth part 33 and the end of the teeth insulation part 43 of the stator 6 adjacent to each other. By being located between the teeth part 33 and the end of the teeth insulation part 43, the plurality of wall parts 50 form the side surface of the cylindrical closed space along with the teeth part 33 and the end of the teeth insulation part 43.
Similarly, the second protective member 20b includes a lid part 61 having a substantially cylindrical outer circumference and a plurality of wall parts 60 extending from the outer circumference of the lid part 61 in the axial direction. The lid part 61 forms the end face of the cylindrical closed space that houses the rotor 7. A shaft guide hole in which the shaft 12 is inserted is formed in the lid part 61. The wall parts 60 are stuck between the teeth part 33 and the end of the teeth insulation part 43 of the stator 6 adjacent to each other. By being located between the teeth part 33 and the end of the teeth insulation part 43, the plurality of wall parts 60 form the side surface of the cylindrical closed space along with the teeth part 33 and the end of the teeth insulation part 43.
A latching part 53 of the wall part 50 in the first protective member 20a and a latching part 63 of the wall part 60 in the second protective member 20b are structured to be latched to each other when they abut each other. This fixes the first protective member 20a and the second protective member 20b. The first protective member 20a and the second protective member 20b may be fixed by another means.
For example, the second protective member 20b may not be provided with the wall parts 60 and be comprised only of the lid part 61, the wall parts 50 of the first protective member 20a may be sized to reach the lid part 61 of the second protective member 20b, and the lid part 61 and the ends of the wall parts 50 may be fixed by screws of a nonmagnetic material. Alternatively, the lid part 51 and the wall parts 50 of the first protective member 20a may be separate members, and, similarly, the lid part 61 and the wall parts 60 of the second protective member 20b may be separate members so as to form the protective member 20 from three or more members. The protective member 20 may be formed by the two lid parts 51, 61, and the plurality of joined wall parts in which the wall parts 50 and the wall parts 60 are joined. Alternatively, a pair of opposite ribs may be formed in the housing 2 of the electric power tool 1, and the axial movement of the first protective member 20a and the second protective member 20b may be restricted by locating the first protective member 20a and the second protective member 20b abutting each other between the ribs. In this case, the lid of the first protective member 20a or the second protective member 20b may be omitted so that at least one of the ribs may function as the lid of the protective member 20. Alternatively, a plurality of extensions extending from the rib in the axial direction may be formed so that the extensions may function as the wall parts of the protective member 20.
Fig. 4 shows a cross section of the motor 4 according to the embodiment perpendicular to the axis. Fig. 4 shows a state of the motor 4 severed at the position of the teeth part 33. The latching part 53 of the wall part 50 of the first protective member 20a and the latching part 63 of the wall part 60 of the second protective member 20b are latched between the ends of the adjacent teeth part 33.
By forming the cylindrical closed space, the protective member 20 not only inhibits air from flowing into the space around the rotor 7 but also inhibits the heat generated in the coil part 14 from being conducted to the rotor 7. In the case the rotor 7 includes, as the permanent magnet 19, a neodymium magnet, which is characterized by a low heat resistance, the protective member 20 maintains the stable motor property by reducing heat conduction from the coil part 14 to the rotor 7.
Fig. 5 shows a variation of the protective member 20. The protective member 20 has a space for mounting a bearing 13. By mounting the bearing 13 in the protective member 20, the dust tightness of the bearing 13 is improved.
Described above is an explanation based on an exemplary embodiment. The embodiment is intended to be illustrative only and it will be understood by those skilled in the art that various modifications to constituting elements and processes could be developed and that such modifications are also within the scope of the present disclosure.
Although it is described in the embodiment that the protective member 20 forms the cylindrical closed space that houses the rotor 7, a heat dissipating hole for venting the heat in the closed space to outside may be provided in the cylindrical closed space. For the purpose of restricting the inflow of air from outside into the cylindrical closed space, the heat dissipating hole may be formed in the direction perpendicular to the direction of travel of air flow caused by the fan 3. For example, the heat dissipating hole may be formed by providing a gap in the portion of latching between the first protective member 20a and the second protective member 20b.
In the electric power tool 1 according to the embodiment, the fan 3, the motor 4, and the circuit board 5 are arranged in the stated order from the back side, but the arrangement may be as desired. For example, the circuit board 5, the motor 4, and the fan 3 may be arranged in this order from the back side. Alternatively, the circuit board 5 may be located at a position distanced from the shaft 12.
In the case the fan 3 is located substantially at the axial center in the housing 2, the directions of intake and discharge of air may be reversed.
Fig. 1 shows that the shaft 12 is rotatably supported by the two bearings 13a, 13b. For example, the bearing 13a may be fixed to the housing 2, and the bearing 13b may be fixed to a motor mount. The insulator 41 according to the embodiment is formed such that the two insulator parts 41a, 41b sandwich the stator core 31 from above and below, but the stator core 31 and the insulator 41 may be molded as an integrated unit.
One embodiment of the present disclosure is summarized below.
A motor (4) according to an embodiment of the disclosure may include: a stator core (31) including an annular yoke part (32) and a plurality of teeth parts (33) projecting from an inner circumferential surface of the yoke part; an insulator (41) that covers the yoke part and the teeth part; a coil (14) wound around the insulator (41) that covers the teeth part; a rotor (7) located inward of the stator core across a predetermined interval from an end of the teeth part; and a protective member (20) located between the yoke part and the rotor and housing the rotor.
The protective member (20) may be configured to include a lid (51, 61) and a plurality of wall parts (50, 60) extending from the lid in an axial direction. The wall parts (50, 60) may be located between ends of adjacent teeth parts. The end of the teeth part and the protective member may form a substantially closed space that houses the rotor.
An electric power tool (1) according to another embodiment of the present disclosure includes, in a housing (2), a fan (3), a brushless motor (4), and a driving block (8) that includes a power transmission unit for transmitting a rotational force of the brushless motor to a front-end tool. The brushless motor may include: a stator core (31) including an annular yoke part (32) and a plurality of teeth parts (33) projecting from an inner circumferential surface of the yoke part; an insulator (41) that covers the yoke part and the teeth part; a coil (14) wound around the insulator (41) that covers the teeth part; a rotor (7) located inward of the stator core across a predetermined interval from an end of the teeth part; and a protective member (20) located between the yoke part and the rotor and housing the rotor. It is preferred that the fan (3) be located outward of the protective member (20).

Claims

A brushless motor (4) comprising:
a stator core (31) including an annular yoke part (32) and a plurality of teeth parts (33) projecting from an inner circumferential surface of the yoke part;

an insulator (41) that covers the yoke part and the teeth part;

a coil (14) wound around the insulator that covers the teeth part;

a rotor (7) located inward of the stator core across a predetermined interval from an end of the teeth part; and

a protective member (20) located between the yoke part and the rotor and housing the rotor.
The brushless motor according to claim 1, wherein the protective member (20) includes a lid (51, 61) and a plurality of wall parts (50, 60) extending from the lid in an axial direction.
The brushless motor according to claim 2, wherein the wall parts (50, 60) are located between ends of adjacent teeth parts.
The brushless motor according to any one of claims 1 through 3, wherein an end of the teeth part and the protective member form a substantially closed space that houses the rotor.
An electric power tool (1) including, in a housing (2), a fan (3), a brushless motor (4), and a driving block (8) that includes a power transmission unit for transmitting a rotational force of the brushless motor to a front-end tool, wherein
the brushless motor (4) includes:
a stator core (31) including an annular yoke part (32) and a plurality of teeth parts (33) projecting from an inner circumferential surface of the yoke part;

an insulator (41) that covers the yoke part and the teeth part;

a coil (14) wound around the insulator that covers the teeth part;

a rotor (7) located inward of the stator core across a predetermined interval from an end of the teeth part; and

a protective member (20) located between the yoke part and the rotor and housing the rotor.
The electric power tool according to claim 5,
wherein the fan (3) is located outward of the protective member (20).